Protective coatings



United States Patent 3,056,684 PROTECTIVE COATINGS Stanley L. Lopata, Ladue, and William R. Keithler, Kirkwood, M0., assignors to Carboline Company, St. Louis, Mo., a corporation of Missouri No Drawing. Filed June 4, 1959, Ser. No. 817,980 24 Claims. (Cl. lilo-14) This invention relates in general to protective coatings and, more particularly, to coatings adapted for application to ferrous surfaces for the protection of such surfaces by selective galvanic action.

It is well recognized that ferrous materials can be protected against corrosion by being placed in juxtaposition to metals which are above iron in the electromotive series, such as, for example, zinc, magnesium, and alu rninum. For example, steel piling which is immersed in sea water along water front installation can be protected by placing large blocks of magnesium or znic in immediate proximity to the piling so that the latter metals are eaten away by a process of what is sometimes referred to as selective galvanic action. In other words, when two different metals are present in a corrosive environment, the corrosive reactions take place selectively upon the metal which is highest in the electroruotive series. A somewhat similar system of anti-corrosion protection has been developed for iron pipes which are laid in the ground. Consequently, some efforts have been made to develop paint-like coatings containing metals which are above iron in the electromotive series.

This type of surface protection involves quite different principles than the use of paints having lead oxide, zinc oxide, titanium dioxide, and copper oxide pigments for the reason that such paints rely upon the fact that the oxide pigments being already fully oxidized cannot be further attacked by atmospheric oxygen. Such oxide pigmented paints, however, form a continuous coating and as soon as the coating [becomes broken, the surface protective character of the coating diminishes rapidly. In this connection, it is also obvious that the oxide pigments are incapable of any selective galvanic action. It is, there fore, highly desirable to provide a means by which metals, such as zinc, aluminum, and magnesium, in elemental form, can be applied to ferrous surfaces in the form of a coating, such that protective advantage can be taken of selective galvanic action. The problem lies in finding an appropriate vehicle in which metallic powder can be incorporated. It is necessary that such coatings be hard and abrasion-resistant and, at the same time, be sufficiently flexible and adherent to the metallic surface so as to establish a permanent protective film which will not flake off or craze as a result of expansion, contraction, vibration, and similar mechanical stresses. It is also desirable that the resin have a reasonably satisfactory shelf-life so that the coating can be compounded and stored for reasonable periods of time.

It is, therefore, the primary object of the present invention to provide a protective coating for ferrous surfaces which utilizes powdered metallic zinc in a vehicle which permits galvanic action to take place.

It is another object of the present invention to provide a coating of the type stated which has relatively long shelf-life and which can be readily applied to a ferrous surface in the manner of a paint.

It is also an object of the present invention to provide a coating of the type stated which sets up on the ferrous surface in a hard, abrasion-resistant, tightly adherent somewhat permeable film.

With the above and other objects in View, our invention resides in the novel means and processes of matter presently described and pointed out in the claims.

Broadly speaking, the present invention resides in the Such coatings can be applied to ferrous surfaces by brushing, spraying, or any other conventional paint-application technique and will set up or air-dry, so to speak, in a reasonably short length of time to form a tightly adhering, hard, tough, semipermeable coating which protects the ferrous surface against attack in a highly corrosive atmosphere by the process of selective galvanic action.

When an excess of water is added to tetraethyl orthosilicate, that is to say an amount in excess of the equivalent weight, the silicate is completely hydrolyzed rather quickly, somewhat according to the following reaction:

The alcohol evaporates, leaving a granular sandy residue. However, when less than an equivalent Weight of water is present, the product is a homogeneous liquid. Actual experiments have shown that vehicles suitable for use in terms of the present invention can be obtained using quantities of water ranging from .25 to .99 equivalent weights. Of course, there is a strong tendency for this hydrolysis reaction to absorb water from atmosphere. Therefore, if the reaction is carried out in a humid atmosphere using exactly .99 equivalent weights of water, enough water is likely to be absorbed from the air, particularly on a humid day, to throw the reaction into a complete hydrolysis. Thus, for practical reasons, it is not desirable to use more than .95 equivalent weights of .Water.

Presumably, the partial hydrolysis of tetraethyl ortho silicate proceeds somewhat according to the following chemical reactions:

The above are merely illustrative and are not presented as positive reactions, since the amount of water present may vary within the ranges above indicated, with the result that the siloxane chain will vary in length.

As this step-wise hydrolysis is continued, condensed esters of higher and higher molecular weight are formed. For purposes of the present invention, the hydrolytic reaction is carried out with limited amounts of water in the pH range above-mentioned until polymers are formed having a chain-length averaging to silicon atoms. In other words, the hydrolysis of the tetraethyl orthosilicate may be said to have been carried from 25% to 95% toward completion.

The partial hydrolysis of tetraethyl orthosilicate can be carried out by dissolving tetraethyl orthosilicate in an organic solvent, such as denatured alcohol, ethylene gly col monoethyl ether, ethylene glycol monoethyl ether acetate, and polyethylene glycols. The pH of this solution is then adjusted to the pH range of 1.5 to 4.0 by the addition of any conventional acid. Thereupon, a quantity of water is added to the solution, such quantity being less than an equivalent weight with respect to the quantity of tetraethyl orthosilicate present. Upon the addition of water, the solution is stirred and, within approximately ten to fifteen minutes, it will be evident that a definite exothermic reaction has been initiated. As a result, the solution becomes quite warm. This temperature rise continues until the water has been completely used up and no further hydrolysis will take place. At this point, the temperature becomes constant for a short period of time and then begins to drop otf gradually. When the temperature begins to drop off, it is evident that the hydrolysis reaction has been concluded and the tetraethyl orthosilicate has been partially hydrolyzed to the degree consonant with the particular limited quantity of water used in the reaction. The resulting product is a homogeneous, somewhat oily, liquid.

The liquids resulting from the foregoing partial hydrolysis are mixed with a filler-component consisting essentially of finely divided metal powders to form the coating material. It has also been found that carbon black, zinc chloride, and fibrous fillers can be added to obtain additional desirable physical characteristics in the finished coating. By way of example and not by way of limitation, the following specific formulas have been found to be highly successful:

Example I Parts by weight Partially hydrolyzed tetraethyl orthosilicate 10 Zinc powder (300 mesh) 70 Example 11 Partially hydrolyzed tetraethyl orthosilicate 30 Zinc powder (300 mesh) 80 Example III Partially hydrolyzed tetraethyl orthosilicate 5 Zinc powder (300 mesh) 30 Example IV Partially hydrolyzed tetraethyl orthosilicate 5 Zinc powder (300 mesh) Example V Partially hydrolyzed tetraethyl orthosilicate 10 Zinc powder (300 mesh) 70 Carbon powder 1 Example VI Partially hydrolyzed tetraethyl orthosilicate 30 Zinc powder (300 mesh) 80 Calcium silicate (fibrous) 3 Example VII Partially hydrolyzed tetraethyl orthosilicate 10 Zinc powder (300 mesh) 60 Carbon powder -2 1 Calcium silicate 2 It has also been found that the addition of an amount equal to 5 to 30% of the partially hydrolyzed tetraethyl orthosilicate of zinc chloride, magnesium chloride, or similar acid-metal salt improves the hardness and toughness of the final film. Some illustrative formulations are as follows:

Example XII Parts by weight Partially hydrolyzed tetraethyl orthosilicate 25 Zinc powder (300 mesh) 65 Zinc chloride (25% solution in ethyl alcohol) 10 Example XIII Partially hydrolyzed tetraethyl orthosilicate 20 Zinc powder (300 mesh) 50 Calcium silicate 5 Magnesium chloride (10% solution in ethyl alcohol) 5 Example XIV Partially hydrolyzed tetraethyl orthosilicate 25 Zinc powder (300 mesh) 60 Asbestos 3 Zinc chloride (25% solution in ethyl alcohol) 5 Carbon 2 It is theorized that the metallic chlorides, such as zinc chloride, for example, forms something in the nature of a chelate or complex with the partially hydrolyzed tetraethyl orthosilicate as follows:

It has been found, in connection with the present invention, that the type of zinc powder and the degree to which the tetraethyl orthosilicate is hydrolyzed affects the character of the product. For example, various types of commercially available zinc powders contain small amounts of alkaline impurities which cause the zinc powder to form a somewhat alkaline slurry when stirred up in distilled water (e.g. a pH ranging from slightly over 8.5 to approximately 11.0). On the other hand, zinc powders (usually made from electrolytic zinc) which are of higher purity will form a practically neutral slurry when stirred up in distilled water (e.g. a pH ranging from slightly over 7.0 to approximately 8.0). This difference can be readily ascertained by simply dropping a sample of the zinc powder in distilled water, stirring, and testing with a conventional indicator such as litmus paper.

The relatively neutral zinc powders will form highly effective tough coatings with a vehicle in which the tetraethyl orthosilicate has been partially hydrolyzed in the range of 50% to 95% hydrolysis, in other words, wherein .5 to .95 equivalent weights of water are used in the hydrolysis. Such coating materials (exemplified by Examples I to IV, inclusive, above) have adequate shelflike, or pot-life, as it is sometimes called, and set up or dry in a matter of a few hours. On the other hand, relatively alkaline zinc powders will form effective coating materials with a vehicle in which the partial hydrolysis ranges as low as 25% (exemplified by Example VIII). Coating materials of this latter type, however, have a much shorter pot-life. When hydrolysis is 75% or more, the alkaline zinc coatings tend to surface crack on drying.

The coating materials containing carbon powder commercially referred to as carbon black (exemplified by Examples VII, IX, and X) may be formulated with vehicles in which the partial hydrolysis of the tetraethyl orthosilicate ranges from 25% to 95%. Coating materials of this type are all hard, tough, and adherent.

It should be understood that changes in the methods, compositions, and combination above set forth may be made without departing from the nature and principle of our invention.

Having thus described our invention, what we claim and desire to secure by Letters Patent is:

l. A galvanic action coating material consisting essentially of a filler-component capable of promoting galvanicprotection of a surface to which the coating material is applied, said filler-component being uniformly dispersed throughout and suspended in a homogeneous liquid vehicle which will form a film that is capable, when dry, of permitting permeation of a suflicient amount of moisture to establish galvanic-action between the filler-component and the surface to which the coating material is applied, said vehicle consisting of tetraethyl orthosilicate which has been partially hydrolyzed by the addition thereto of a selected quantity of water which quantity is in the range of .25 to .95 equivalent weights with respect to the quantity of tetraethyl orthosilicate, and said filler-component consisting of powdered zinc.

2. A galvanic action coating material consisting essentially of a filler-component capable of promoting galvanicprotection of a surface to which the coating material is applied, said filler-component being uniformly dispersed throughout and suspended in a homogeneous liquid vehicle which will form a film that is capable, when dry, of permitting permeation of a sufficient amount of moisture to establish galvanic-action between the filler-component and the surface to which the coating material is applied, said vehicle consisting of tetraethyl orthosilicate which has been partially hydrolyzed by the action thereto of a selected quantity of water which quantity is in the range of .25 to .95 equivalent weights with respect to the quantity of tetraethyl orthosilicate, said filler-component consisting of powdered zinc and powdered carbon.

3. A galvanic-action coating material consisting essentially of a filler-component capable of promoting galvanicprotection of a surface to which the coating material is applied, said filler-component being uniformly dispersed throughout and suspended in a homogeneous liquid vehicle which will form a film that is capable, when dry, of permitting permeation of a sufiicient amount of moisture to establish galvanic-action between the filler-component and the surface to which th coating material is applied, said vehicle consisting of tetraethyl orthosilicate which has been partially hydrolyzed by the addition thereto of a selected quantity of water which quantity is in the range of .25 to .95 equivalent weights with respect to the quantity of tetraethyl orthosilicate, said filler-component consisting of powdered zinc and a fibrous-material of the class consisting of calcium silicate and asbestos.

4. A galvanic-action coating material consisting essentially of a filler-component capable of promoting galvanicprotection of a surface to which the coating material is applied, said filler-component being uniformly dispersed throughout and suspended in a homogeneous liquid vehicle which will form a film that is capable, when dry, of permitting permeation of a sufficient amount of moisture to establish galvanic-action between the filler-component and the surface to which th coating material is applied, said vehicle consisting of tetraethyl orthosilicate which has been partially hydrolyzed by the addition thereto of a selected quantity of water which quantity is in the range of .25 to .95 equivalent weight with respect to the quantity of tetraethyl orthosilicate, said filler-component consisting of powdered zinc and zinc chloride.

5. A galvanic-action coating material consisting essentially of a filler-component capable of promoting galvanicprotection of a surface to which the coating material is applied, said filler-component being uniformly dispersed throughout and suspended in a homogeneous liquid vehicle which will form a film that is capable, when dry, of permitting permeation of a sufficient amount of moisture to establish galvanic-action between the filler-component and the surface to which the coating material is applied, said vehicle consisting of tetraethyl orthosilicate which has been partially hydrolyzed by the addition thereto of a selected quantity of water which quantity is in the range of .25 to .95 equivalent weights with respect to the quantity of tetraethyl orthosilicate, and said fillercomponent consisting of powdered Zinc, powdered carbon and zinc chloride.

6. A galvanic-action coating material consisting essentially of a filler-component capable of promoting galvanicprotection of a surface to which the coating material is applied, said filler-component being uniformly dispersed throughout and suspended in a homogeneous liquid vehicle which will form a film that is capable, when dry, of permitting permeation of a suflicient amount of moisture to establish galvanic-action between the filler-component and the surface to which the coating material is applied, said vehicle consisting of tetraethyl orthosilicate which has been partially hydrolyzed by the addition thereto of a selected quantity of water which quantity is in th range of-.25 to .95 equivalent weights with respect to the quantity of tetraethyl orthosilicate, and said filler-component consisting of powdered zinc, powdered carbon and a fibrous material of the class consisting of calcium silicate and asbestos.

7. A galvanic action coating material consisting essentially of a filler-component capable of promoting galvanicprotection of a surface to which the coating material is applied, said filler-component being uniformly dispersed throughout and suspended in a homogeneous liquid vehicle which will form a film that is capable, when dry, of permitting permeation of a sufficient amount of moisture to establish galvanic-action between the filler-component and the surface to which the coating material is applied, said vehicle consisting of tetraethyl orthosilicate which has been partially hydrolyzed by the addition thereto of a selected quantity of water which quantity is in the range of .25 to .95 equivalent weights with respect to the quantity of tetraethyl orthosilicate, and said fillercomponent consisting of powdered zinc, powdered carbon, zinc chloride and a fibrous material of the class consisting of calcium silicate and asbestos.

8. A galvanic action coating material consisting essentially of a filler-component capable of promoting galvanicprotection of a surface to which the coating material is applied, said filler-component being uniformly dispersed throughout and suspended in a homogeneous liquid vehicle which will form a film that is capable, when dry, of permitting permeation of a sufiicient amount of moisture to establish galvanic-action between the filler-component and the surface to which the coating material is applied, said vehicle consisting of a liquid tetraethyl siloxane polymer having a chain-length averaging tosilicon atoms and resulting from the partial hydrolysis of tetraethyl orthosilicate by the addition thereto of av selected quantity of water which quantity is in the range of .25 to .95 equivalent weights with respect to the quantity of tetraethyl orthosilicate, and said filler-component con sisting essentially of powdered Zinc.

9. A coating material according to claim 8 in which the powdered Zinc is present in an amount ranging from 1 part polymer and 2 parts zinc to 1 part polymer and 7 parts zinc.

10. A coating material according to claim 8 in which the filler-component consists of powdered zinc and zinc chloride.

11. A coating material according to claim 1 in which the relative parts by weight of vehicle and filler-component are as follows:

Parts by weight Liquid vehicle tetraethyl orthosilicate 10 Zinc powder (300 mesh) 70 12. A coating material according to claim 1 in which the relative parts by weight of vehicle and filler-component are as follows:

Parts by weight Liquid vehicle tetraethyl orthosilicate 5 Zinc powder (300 mesh) 30 13. A coating material according to claim 1 in which the relative parts by weight of vehicle and filler-component are as follows:

Parts by weight Liquid vehicle tetraethyl orthosilicate 5 Zinc powder (300 mesh) 20 14. A coating material according to claim 2 in which the relative parts by weight of vehicle and filler-component are as follows:

Parts by weight Liquid vehicle tetraethyl orthosilicate 10 Zinc powder (300 mesh) 70 Carbon powder 1 15. A coating material according to claim 6 in which the relative parts by Weight of vehicle and filler-component are as follows:

Parts by weight Liquid vehicle tetraethyl orthosilicate 10 Zinc powder (300 mesh) 60 Carbon powder 1 Calcium silicate 2 16. A coating material according to claim 1 in which the relative parts by weight of vehicle and filler-component are as follows:

Parts by weight Liquid vehicle tetraethyl orthosilicate Zinc powder (300 mesh) 50 17. A coating material according to claim 3 in which the relative parts by weight of vehicle and filler-component are as follows:

Parts by weight Liquid vehicle tetraethyl orthosilicate Zinc poWder (300 mesh) 6O Fibrous asbestos 2 19. A coating material according to claim 7 in which the relative parts by weight of vehicle and filler-component are as follows:

Parts by weight Liquid vehicle tetraethyl orthosilicate 25 Zinc powder (300 mesh) 60 Asbesto 3 Zinc chloride (25% solution in ethyl alcohol) 5 Carbon 2 20. The method of making a galvanic action coating which comprises dissolving tetraethyl orthosilicate in an organic solvent, adding a quantity of acid to the solution whereby to adjust the pH to the range of 1.5 to 4.0, adding a quantity of water to the solution, such quantity being in the range of .25 to .95 of an equivalent weight with respect to the quantity of tetraethyl orthosilicate to produce a liquid siloxane having an average chain length of 5 to 10 silicon atoms, agitating th mixture until an exothermic reaction is initiated, continuing agitation until the exothermic reaction is completed and the temperature of the solution begins to drop off, and adding finely divided zinc to the resulting fluid.

21. A coating material according to claim 3 in which the relative parts by weight of vehicle and filler-component are as follows:

Parts by weight Liquid vehicle tetraethyl orthosilicate 30 Zinc powder (300 mesh) Calcium silicate (fibrous) 3 22. A coating material according to claim 2 in which the relative parts by weight of vehicle and filler-component are as follows:

Parts by weight Liquid vehicle tetraethyl orthosilicate 10 Zinc powder 300 mesh) 40 Carbon powder 2 g 23. A coating material according to claim 6 in which the relative parts by weight of vehicle and filler-component are as follows:

Parts by weight Liquid vehicle tetraethyl orthosilicate 30 Zinc powder (300 mesh) 70 Carbon powder 3 Calcium silicate (fibrous) 5 24. A coating material according to claim 4 in which the relative parts by weight of vehicle and filler-component are as follows:

Parts by weight Liquid vehicle tetraethyl orthosilicate 25 Zinc powder (300 mesh) 65 Zinc chloride (25 solution in ethyl alcohol) 10 References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Gardner: Educational Bureau, Scientific Section, Paint Manufacturers Association of the U.S., Circular No. 61, issued April 1919, page 1.

Metallic Zinc in Rust Inhibitive Paints, Metal Cleaning and Finishing, vol. 6, No. 4, April 1934, pages 198 and 199.

Dedication 3,056,684.Stcmley L. Lopato, Ladue, and William 13. Kez'thlm", Kirkwood,

M0. PROTECTIVE COATINGS. Patent dated Oct. 2, 1962. Dedication filed Oct. 16, 197 2, by the assignee, Oarboline Company.

Hereby dedicates to the Public the entire renmining' term of said patent.

[Oficial Gazette JCZWUGTIZ/ 30, 1973.] 

1. A GALVANIC ACTION COATING MATERIAL CONSISTING ESSENTIALLY OF A FILLER-COMPONENT CAPABLE OF PROMOTING GALVANICPROTECTION OF A SURFACE TO WHICH THE COATING MATERIAL IS APPLIED, SAID FILLER-COMPONENT BENG UNIFORMLY DISPERSED THROUGHOUT AND SUSPENDED IN A HOMOGENEOUS LIQUID VEHICLE WHICH WILL FORM A FILM THAT IS CAPABLE, WHEN DRY, OF PERMITTING PERMEATION OF A SUFFICIENT AMOUNT OF MOISTURETO ESTABLISH GALVANIC-ACTION BETWEEN THE FILER-COM PONENT AND THE SURFACE TO WHICH THE COATING MATERIAL IS APPLIED, SAID VEHICLE CONSISTING OF TETRAETHYL ORTHOSILICATE WHICH HAS BEEN PARTIALLY HYDROLYZED BY THE ADDITION THERETO OF A SELECTED QUANTITY OF WATER WHICH QUANTITY IS IN THE RANGE OF .25 TO .95 EQUIVALENT WEIGHTS WITH RESPECT TO THE QUANTITY OF TETRAETHYL ORTHOSILICATE, AND SAID FILLER-COMPONENT CONSISTING OF POWDERED ZINC. 